This invention relates generally to the field of medical devices, and more particularly to a system and method which includes an implantable pulse generator.
Implantable pulse generators have been successfully used to treat patients having a variety of cardiac condition. For example, cardioverter/defibrillators (ICDs) have been successfully used to treat patients who have experienced one or more documented episodes of hemodynamically significant ventricular tachycardia or ventricular fibrillation. Implantable cardiac pacemakers have been successfully used to treat patients having a variety of cardiac rhythm management problems, including slow heart rates (symptomatic bradycardia) and in cases where the patient""s AV node is irreversibly disabled.
The basic implantable pulse generator consists of a primary battery, electronic circuitry to control both the sensing of the patient""s cardiac signals and the delivery of electrical shocks to the patient""s heart, and one or more capacitors housed within a hermetically sealed titanium case. One or more catheter leads having electrodes are implanted within the heart of the patient or on the epicardial surface of the patient""s heart. The catheter leads are then coupled to the implantable housing and the electronic circuitry of the implantable pulse generator and are used to deliver electrical energy to the heart.
The cardiac lead of the implantable pulse generator are used to sense cardiac complexes in and around the heart of the patient. Cardiac complexes generate a very weak current that must be amplified prior to being analyzed by the electronic circuitry of the implantable pulse generator. In addition to cardiac complexes, however, many signals unrelated to the cardiac complex, such as current due to pectoral muscle activity or external electromagnetic interference, cause additional weak currents in the implantable pulse generator system. These extraneous currents can be amplified and analyzed the by the electronic circuitry of the implantable pulse generator. When this happens there is the possibility that the extraneous signals could cause the implantable pulse generator to either inhibit necessary therapy or initiate inappropriate therapy to the patient.
To reduce the possibility that these currents will be inappropriately sensed as cardiac complexes, additional components are added to the sensing circuit. One is a level detector to prevent low-level electrical noise from being sensed. The other is a bandpass filter to help eliminate stronger signals that are of a different frequency than those associated with the cardiac complexes. While these additional components are helpful in reducing or eliminating some types of noise there exists noise signals sufficiently strong to overcome these components. For example, electromagnetic interference from certain types of machinery and equipment can be sufficient to create noise in an implantable pulse generator. When this happens noise is detected by the implantable pulse generator.
Implantable pulse generators interact with medical device programmers to transfer data and operating instructions between the two devices. The typical programmer is a microprocessor-based unit that has a wand for creating the telemetric link between the implanted pulse generator and the programmer, and a graphics display screen that presents a patient""s recorded cardiac data and implantable pulse generator system information to the physician.
Typically, the physician will use the medical device programmer in a clinical setting where electromagnetic interference can be especially prevalent. During these clinical settings the operation (or the function) of the implantable pulse generator is tested with the medical device programmer. If an electromagnetic field is effecting the performance of the implantable pulse generator during this time, parameter settings for the implantable pulse generator my be incorrectly set due to the influence of the electromagnetic field. This could lead to a potentially dangerous situation for the patient.
For the reasons stated above, and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for a system which is capable of signaling to a user the existence of noise presently being detected by an implantable pulse generator.
As explained in detail below, the present subject matter is directed to a system and method for the analysis and detection of noise in one or more cardiac signals sensed by an implantable pulse generator. As noise is detected in the one or more cardiac signals markers indicating the present of the noise are displayed to a user interacting with the implantable pulse generator. Thus, the present subject matter provides an advantage by providing information to an operator of the medical device programmer that noise is present on the sensing channels of the device and exactly what therapies are being delivered, or suppressed, because of the noise.
In one embodiment, at least one cardiac signal is sensed with an implantable pulse generator. Cardiac depolarizations are identified in the at least one cardiac signal and cardiac depolarization markers are generated. The at least one cardiac signals are then analyzed for a noise event during a refractory period following the detected cardiac depolarization. The refractory period includes a noise window interval during which noise events are recognized. When a noise event, or events, occur during the noise window interval a first noise marker is generated. The noise window interval is then repeated as long as noise is detected in the noise window intervals. When the noise persists for a predetermined time interval a second noise marker is generated.
A communication link is established between the implantable pulse generator and a medical device programmer. The at least one cardiac signal is transmitted from the implantable pulse generator to the medical device programmer. As the at least one cardiac signal is received, the medical device programmer displays the signal(s) on a display screen. In addition to displaying the cardiac signal(s), the medical device programmer also displays the cardiac depolarization marker, the first noise marker and the second noise marker on the display screen. In one embodiment, the markers are associated with the approximate location of where the event giving rise to the marker occurred. Additionally, the cardiac signal(s) and the markers may also be printed on paper.
These and other features and advantages of the invention will become apparent from the following description of the preferred embodiments of the invention.